Originally Posted by John Hilley
This doesn't make sense either. If the CPAP takes 1 amp on 120 VAC, it should take close to 10 amps on 12 VDC. There could be a little lost with the 120 VAC conversion, but not much.
True story: I used to think MSW inverters were more efficient than True Sine till I researched.. So what did I find.
I looked at TWO Xantrex converters. One a Prosine (true sine) and one a X-power (MSW) as it happens I have one of each here but NOT the specific ones I looked at.
I made sure they were the same size (Apples to as they say)
The X-power had a peak efficiency of 90%
The Prosine 89-90 percent
So based on that a 120 volt device drawing 1 amp will need a MINIMUM (Not both cases it was BEST) of 11 amps at 12 volt to feed the inverter
This is a guess. But I am guessing peak efficiency happens close to maximum load. (That would be 1500 watts on the two I compared)
I normally say that the 12 volt amp draw is = to the 120 volts WATTS/10
Now I know that is not accurate.. but as it turns out it is very close for anything under 1,000 watts.